I don't think he's talking about selling mods . . .
. . to GPL'd software, but about Web services sites having competitive advantage by using proprietary mods on top of a GPL'd base.
The proposed GPLv3 specifically negates this advantage in favor of returning those mods to the community.
While he certainly has a point, that point is from a programmer's perspective, precisely the perspective that doomed the Dot.Com "economy". It really doesn't matter.
The success of a Web services business will depend on what it offers and how well it offers it. Coding is only peripheral because these are designer and marketing factors. The coding just has to be competent.
His fears are ghosts because design and presentation are everything. The guy with great presentation and so-so code will devestate the guy with poor presentation and wonderful code every time until Hell freezes over, and probably for a long time after.
If the guy with great design and presentation also has great code - he'll be a legend. Let the world download his code. Let him say, "Hey world, here's my code, secret of my success, come and get it!". It'll keep 'em from figuring out what he's really doing.
GPLv3 is not the end of the world.
